The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Modern passenger car and truck hybrid automatic transmissions frequently employ high torque electric motors to act as the sole energy source in certain operational modes and to operate in conjunction with a gasoline, Diesel or flexible fuel engine in other operational modes. Because these electric motors generate significant mechanical power for lengthy periods of time while consuming corresponding quantities of electrical power, they generate significant amounts of heat. In order to maintain a suitable, low operating temperature, it is necessary to remove such heat, typically by circulation of a heat transfer medium around the motor housing. Given the availability of transmission fluid, its system for circulation and heat rejection and its acknowledged heat transfer function, it is the obvious general solution to this requirement.
Because of the presence of pressurized or unpressurized moving fluid nearly everywhere within an automatic transmission, a first solution might appear to be simply exposing the motors to fluid circulating in the transmission. In reality, such fluid circulation at any given location within the transmission may vary widely depending upon the current operating state of the transmission and compromise cooling of the motor under certain conditions. It is thus apparent that a controlled, dedicated flow of transmission fluid to cool the motor is desirable.
However, due to the importance of maintaining relatively cool motor temperatures under all operating conditions with large motors occupying much or all of the transmission cross section, and the need to both positively provide fluid flow and control the volume of fluid flow, the choice to utilize a dedicated flow of transmission fluid for cooling creates a new array of engineering challenges. A first challenge relates to the fact that the motors may occupy all or a significant portion of the cross section of the transmission. This creates difficulties relating to fluid distribution to and within the motor. One solution to this challenge is to provide pressurized fluid to an annular passageway disposed between the motor housing and the inside of the transmission housing. Radial ports in the motor housing direct fluid to motor components such as the windings to absorb and carry away heat. A related challenge involves providing a secure, fluid tight seal between the transmission housing and motor housing so that a consistent, controlled flow of transmission fluid through the motor and its windings can be achieved.
One prior art approach to achieving a seal between a transmission and a drive motor housing utilizes O-rings disposed in channels extending about the circumference of the motor housing that engage complementarily located and configured circular shoulders or surfaces in the transmission housing. While this arrangement provides an acceptable seal, it is subject to assembly variations. For example, since the O-rings are installed on the outside of the motor housing, they are subject to being accidentally dislodged before or during mounting of the motor. Additionally, if an O-ring comes in contact with, for example, a sharp edge of the transmission housing during mounting of the motor, minor and possibly undetected damage to the O-ring can occur, resulting in initial or premature seal failure. Additionally, verification that the O-ring is assembled is very difficult due to its small size relative to the motor assembly. This precludes use of a vision system to ensure the O-ring is in place prior to assembly into the main housing.
From the foregoing brief review of the prior art of drive motor/transmission seal technology, it is apparent that improvements to this art are desirable.